MPK3/6-induced degradation of ARR1/10/12 promotes salt tolerance in Arabidopsis
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ABSTRACT: Cytokinins are phytohormones that regulate plant development, growth, and responses to stress. In particular, cytokinin has been reported to negatively regulate plant adaptation to high salinity; however, the molecular mechanisms that counteract cytokinin signaling and enable salt tolerance are not fully understood. Here, we provide evidence that salt stress induces the degradation of the cytokinin signaling components Arabidopsis (Arabidopisis thaliana) response regulator 1 (ARR1), ARR10 and ARR12. Furthermore, the stress-activated mitogen activated protein kinase 3 (MPK3) and MPK6 interact with and phosphorylate ARR1/10/12 to promote their degradation in response to salt stress. As expected, salt tolerance is decreased in the mpk3/6 double mutant, but enhanced upon ectopic MPK3/MPK6 activation in an MKK5DD line. Importantly, salt hypersensitivity phenotypes of the mpk3/6 line were significantly alleviated by mutation of ARR1/12. The above results indicate that MPK3/6 enhance salt tolerance in part via their negative regulation of ARR1/10/12 protein stability. Thus, our work reveals a new molecular mechanism underlying salt-induced stress adaptation and the inhibition of plant growth, via enhanced degradation of cytokinin signaling components.
Project description:Cytokinins are phytohormones that regulate plant development, growth, and responses to stress. In particular, cytokinin has been reported to negatively regulate plant adaptation to high salinity; however, the molecular mechanisms that counteract cytokinin signaling and enable salt tolerance are not fully understood. Here, we provide evidence that salt stress induces the degradation of the cytokinin signaling components Arabidopsis (Arabidopisis thaliana) response regulator 1 (ARR1), ARR10 and ARR12. Furthermore, the stress-activated mitogen-activated protein kinase 3 (MPK3) and MPK6 interact with and phosphorylate ARR1/10/12 to promote their degradation in response to salt stress. As expected, salt tolerance is decreased in the mpk3/6 double mutant, but enhanced upon ectopic MPK3/MPK6 activation in an MKK5DD line. Importantly, salt hypersensitivity phenotypes of the mpk3/6 line were significantly alleviated by mutation of ARR1/12. The above results indicate that MPK3/6 enhance salt tolerance in part via their negative regulation of ARR1/10/12 protein stability. Thus, our work reveals a new molecular mechanism underlying salt-induced stress adaptation and the inhibition of plant growth, via enhanced degradation of cytokinin signaling components.
Project description:High levels of boron (B) induce DNA double-strand breaks (DSBs) in eukaryotes, including plants. Here we show a molecular pathway of high B-induced DSBs by characterizing Arabidopsis thaliana hypersensitive to excess boron mutants. Molecular analysis of the mutants revealed that degradation of a SWItch/Sucrose Non-Fermentable subunit, BRAHMA (BRM), by a 26S proteasome (26SP) with specific subunits is a key process for ameliorating high-B-induced DSBs. We also found that high-B treatment induces histone hyperacetylation, which increases susceptibility to DSBs. BRM binds to acetylated histone residues and opens chromatin. Accordingly, we propose that the 26SP limits chromatin opening by BRM in conjunction with histone hyperacetylation to maintain chromatin stability and avoid DSB formation under high-B conditions. Interestingly, a positive correlation between the extent of histone acetylation and DSB formation is evident in human cultured cells, suggesting that the mechanism of DSB induction is also valid in animals.
Project description:Salinity stress challenges agriculture and food security globally. Upon salt stress, plant growth slows down, nutrients are recycled, osmolytes are produced, and reallocation of Na+ takes place. Since autophagy is a high-throughput degradation pathway that contributes to nutrient remobilization in plants, we explored the involvement of autophagic flux in salt stress response of Arabidopsis with various approaches. Confocal microscopy of GFP-ATG8a in transgenic Arabidopsis showed that autophagosome formation is induced shortly after salt treatment. Immunoblotting of ATG8s and the autophagy receptor NBR1 confirmed that the level of autophagy peaks within 30 min of salt stress, and then settles to a new homeostasis in Arabidopsis. Such an induction is absent in mutants defective in autophagy. Within 3 h of salt treatment, accumulation of oxidized proteins is alleviated in the wild-type; however, such a reduction is not seen in atg2 or atg7. Consistently, the Arabidopsis atg mutants are hypersensitive to both salt and osmotic stresses, and plants overexpressing ATG8 perform better than the wild-type in germination assays. Quantification of compatible osmolytes further confirmed that the autophagic flux contributes to salt stress adaptation. Imaging of intracellular Na+ revealed that autophagy is required for Na+ sequestration in the central vacuole of root cortex cells following salt treatment. These data suggest that rapid protein turnover through autophagy is a prerequisite for salt stress tolerance in Arabidopsis.
Project description:Plants have evolved diverse strategies to accommodate saline environments. More insights into the knowledge of salt stress regulatory pathways will benefit crop breeding. RADICAL-INDUCED CELL DEATH 1 (RCD1) was previously identified as an essential player in salt stress response. However, the underlying mechanism remains elusive. Here, we unraveled that Arabidopsis NAC domain-containing protein 17 (ANAC017) acts downstream of RCD1 in salt stress response, and its ER-to-nucleus transport is triggered by high salinity. Genetic and biochemical evidence showed that RCD1 interacts with transmembrane motif-truncated ANAC017 in the nucleus and represses its transcriptional activity. Transcriptome analysis revealed that genes associated with oxidation reduction process and response to salt stress are similarly dysregulated in loss-of-function rcd1 and gain-of-function anac017-2 mutants. In addition, we found that ANAC017 plays a negative role in salt stress response by impairing the superoxide dismutase (SOD) enzyme activity. Taken together, our study uncovered that RCD1 promotes salt stress response and maintains ROS homeostasis by inhibiting ANAC017 activity.
Project description:Polyamines represent a potential source of 4-aminobutyrate (GABA) in plants exposed to abiotic stress. Terminal catabolism of putrescine in Arabidopsis thaliana involves amine oxidase and the production of 4-aminobutanal, which is a substrate for NAD+-dependent aminoaldehyde dehydrogenase (AMADH). Here, two AMADH homologs were chosen (AtALDH10A8 and AtALDH10A9) as candidates for encoding 4-aminobutanal dehydrogenase activity for GABA synthesis. The two genes were cloned and soluble recombinant proteins were produced in Escherichia coli. The pH optima for activity and catalytic efficiency of recombinant AtALDH10A8 with 3-aminopropanal as substrate was 10.5 and 8.5, respectively, whereas the optima for AtALDH10A9 were approximately 9.5. Maximal activity and catalytic efficiency were obtained with NAD+ and 3-aminopropanal, followed by 4-aminobutanal; negligible activity was obtained with betaine aldehyde. NAD+ reduction was accompanied by the production of GABA and β-alanine, respectively, with 4-aminobutanal and 3-aminopropanal as substrates. Transient co-expression systems using Arabidopsis cell suspension protoplasts or onion epidermal cells and several organelle markers revealed that AtALDH10A9 was peroxisomal, but AtALDH10A8 was cytosolic, although the N-terminal 140 amino acid sequence of AtALDH10A8 localized to the plastid. Root growth of single loss-of-function mutants was more sensitive to salinity than wild-type plants, and this was accompanied by reduced GABA accumulation.
Project description:BackgroundPlant growth promoting rhizobacteria (PGPR), such as Bradyrhizobium japonicum IRAT FA3, are able to improve seed germination and plant growth under various biotic and abiotic stress conditions, including high salinity stress. PGPR can affect plants' responses to stress via multiple pathways which are often interconnected but were previously thought to be distinct. Although the overall impacts of PGPR on plant growth and stress tolerance have been well documented, the underlying mechanisms are not fully elucidated. This work contributes to understanding how PGPR promote abiotic stress by revealing major plant pathways triggered by B. japonicum under salt stress.ResultsThe plant growth-promoting rhizobacterial (PGPR) strain Bradyrhizobium japonicum IRAT FA3 reduced the levels of sodium in Arabidopsis thaliana by 37.7%. B. japonicum primed plants as it stimulated an increase in jasmonates (JA) and modulated hydrogen peroxide production shortly after inoculation. B. japonicum-primed plants displayed enhanced shoot biomass, reduced lipid peroxidation and limited sodium accumulation under salt stress conditions. Q(RT)-PCR analysis of JA and abiotic stress-related gene expression in Arabidopsis plants pretreated with B. japonicum and followed by six hours of salt stress revealed differential gene expression compared to non-inoculated plants. Response to Desiccation (RD) gene RD20 and reactive oxygen species scavenging genes CAT3 and MDAR2 were up-regulated in shoots while CAT3 and RD22 were increased in roots by B. japonicum, suggesting roles for these genes in B. japonicum-mediated salt tolerance. B. japonicum also influenced reductions of RD22, MSD1, DHAR and MYC2 in shoots and DHAR, ADC2, RD20, RD29B, GTR1, ANAC055, VSP1 and VSP2 gene expression in roots under salt stress.ConclusionOur data showed that MYC2 and JAR1 are required for B. japonicum-induced shoot growth in both salt stressed and non-stressed plants. The observed microbially influenced reactions to salinity stress in inoculated plants underscore the complexity of the B. japonicum jasmonic acid-mediated plant response salt tolerance.
Project description:BackgroundThe metabolism of hydrogen gas (H(2)) in bacteria and algae has been extensively studied for the interesting of developing H(2)-based fuel. Recently, H(2) is recognized as a therapeutic antioxidant and activates several signalling pathways in clinical trials. However, underlying physiological roles and mechanisms of H(2) in plants as well as its signalling cascade remain unknown.Methodology/principal findingsIn this report, histochemical, molecular, immunological and genetic approaches were applied to characterize the participation of H(2) in enhancing Arabidopsis salt tolerance. An increase of endogenous H(2) release was observed 6 hr after exposure to 150 mM NaCl. Arabidopsis pretreated with 50% H(2)-saturated liquid medium, mimicking the induction of endogenous H(2) release when subsequently exposed to NaCl, effectively decreased salinity-induced growth inhibition. Further results showed that H(2) pretreatment modulated genes/proteins of zinc-finger transcription factor ZAT10/12 and related antioxidant defence enzymes, thus significantly counteracting the NaCl-induced reactive oxygen species (ROS) overproduction and lipid peroxidation. Additionally, H(2) pretreatment maintained ion homeostasis by regulating the antiporters and H(+) pump responsible for Na(+) exclusion (in particular) and compartmentation. Genetic evidence suggested that SOS1 and cAPX1 might be the target genes of H(2) signalling.ConclusionsOverall, our findings indicate that H(2) acts as a novel and cytoprotective regulator in coupling ZAT10/12-mediated antioxidant defence and maintenance of ion homeostasis in the improvement of Arabidopsis salt tolerance.
Project description:BackgroundElongation factor 1 A (EF1A), an essential regulator for protein synthesis, has been reported to participate in abiotic stress responses and environmental adaption in plants. However, the role of EF1A in abiotic stress response was barely studied in Medicago truncatula. Here, we identified elongation factor (EF) genes of M. truncatula and studied the salt stress response function of MtEF1A1 (MTR_6g021805).ResultsA total of 34 EF genes were identified in the M. truncatula genome. Protein domains and motifs of EFs were highly conserved in plants. MtEF1A1 has the highest expression levels in root nodules and roots, followed by the leaves and stems. Transgenic Arabidopsis thaliana overexpressing MtEF1A1 was more resistant to salt stress treatment, with higher germination rate, longer roots, and more lateral roots than wild type plant. In addition, lower levels of H2O2 and malondialdehyde (MDA) were also detected in transgenic Arabidopsis. Similarly, MtEF1A1 overexpressing M. truncatula was more resistant to salt stress and had lower levels of reactive oxygen species (ROS) in leaves. Furthermore, the expression levels of abiotic stress-responsive genes (MtRD22A and MtCOR15A) and calcium-binding genes (MtCaM and MtCBL4) were upregulated in MtEF1A1 overexpressing lines of M. truncatula.ConclusionThese results suggested that MtEF1A1 play a positive role in salt stress regulation. MtEF1A1 may realize its function by binding to calmodulin (CaM) or by participating in Ca2+-dependent signaling pathway. This study revealed that MtEF1A1 is an important regulator for salt stress response in M. truncatula, and provided potential strategy for salt-tolerant plant breeding.